The present invention relates to a method of producing zeolite Y.
It is known that dealuminized Y zeolites with a ratio of SiO.sub.2 /Al.sub.2 O.sub.3 &gt;100 obtained from NaY zeolite by treatment with silicon tetrachloride (DAY-S) have the advantage over aluminum-poor Y-zeolites obtained in other ways that their micropore system is largely intact. Thus, such materials have especially favorable properties for adsorption technology as regards their micropore volume and their selectivity (J. A. Martens, P. J. Grobet, P. A. Jacobs, Preparation of Catalysts V (Stud. Surf. Sci. Catal. 63), Elsevier, Amsterdam 1991, p. 355; WO 88/03437).
Y-zeolites DAY-S with high SiO.sub.2 /Al.sub.2 O.sub.3 ratios of the framework, especially those with &gt;100, have only limited stability under drastic hydrothermal conditions like those which can occur, for example, during the regeneration using water vapor in a few adsorptive and catalytic methods. In addition, they dissolve in aqueous, alkaline systems with clear losses of crystallinity. Measures were therefore developed to subsequently increase the resistance of such zeolites to water vapor and aqueous, alkaline media. For example, the building up of an aluminosilicate layer on the crystals by reacting the zeolites with a sodium aluminate solution of silicon-rich Y zeolites results in protection against water vapor (DD 296 899 and DE 42 07 815).
The prior technique has the disadvantage that the treating of very silicon-rich Y zeolites can cause damage to the crystal structure if a careful procedure is not followed on account of the pH of sodium aluminate solutions, which is in the alkaline range.
The post treatment of Y zeolites very extensively dealuminized with SiCl.sub.4 (aluminum content .ltoreq.1.36%) with water vapor is known. As a result of this, amorphous silicon dioxide is either reinserted into the zeolite framework or converted into crystalline quartz (see G. J. Ray et al., ZEOLITES (1988), vol. 8, page 458 "Characterization of Defects in Deluminated Faujasite").
It is therefore an object of the present invention to produce Y zeolites with SiO.sub.2 /Al.sub.2 O.sub.3 ratios in their framework of &gt;100 which have a high hydrothermal stability and are resistant to alkaline solutions.